High Alumina Low Soda Glass Compositions

ABSTRACT

A glass composition includes a base glass portion comprising: 65-75 wt % SiO2; 5-15 wt % CaO; 0-5 wt % MgO; 0-5 wt % K2O; 10-14 wt % Na2O; and 1-5 wt % Al2O3; wherein the glass composition has a ratio of Na2O to Al2O3 is in the range of 9.5-12.5 wt %/wt %.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/690,663, filed Jun. 27, 2018, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a low-solar-absorbing blue glass, and moreparticularly to a high alumina, low soda glass composition and glasssubstrate.

Technical Considerations

Insulating glass (IG) units are preferred windows in residential andcommercial buildings because they reduce energy transmittance throughthe window. As is appreciated by those skilled in the art, reducingenergy transmittance through the IG unit reduces heat losses from thebuilding interior during the winter, and reduces heat gain to thebuilding interior during the summer. For example, some particular glasscompositions which provide superior optical properties are described inU.S. Pat. Nos. 8,268,741, 6,313,053, and 4,792,536, which are herebyincorporated by reference herein in their entireties.

However, some presently available IG units may be prone to chemicaldamage when stored for an extended period of time. For example, suchglass substrates may become “stained” or corroded due to exposure towater and/or the atmosphere, which may reduce the quality and value ofthe glass, particularly in architectural applications or otherapplications where visual appearance may be of importance.

Accordingly, as can now be appreciated by those skilled in the art, itwould be desirable to provide improved glass compositions which mayincrease the chemical durability of an insulating glass whilemaintaining or improving upon the targeted color, solar absorption, meltcharacteristics, and other optical and/or physical properties thereof.

SUMMARY OF THE INVENTION

In order to address some or all of the above-referenced deficiencies inthe art, the present disclosure provides a high alumina, low soda glasscomposition, which, when used in a low-solar-absorbing blue glasssubstrate (e.g. a glass sheet cut from a glass ribbon made using acontinuous flat glass making process), provides the low-solar-absorbingblue glass substrate with increased chemical durability while allowinglow-solar-absorbing blue glass substrate to substantially maintain itstarget melt characteristics and optical properties.

Accordingly, provided herewith is a glass composition comprising a baseglass portion comprising: 65-75 wt % SiO₂; 5-15 wt % CaO; 0-5 wt % MgO;0-5 wt % K₂O; 10-14 wt % Na₂O; and 1-5 wt % Al₂O₃; wherein the glasscomposition has a ratio of Na₂O to Al₂O₃ is in the range of 9.5-12.5 wt%/wt %. The base glass portion may have a ratio of CaO to MgO in therange of 1.5-2.2 wt %/wt %. The base glass portion may further comprise0.1-0.5 wt % K₂O. The base glass portion may comprise 68-74 wt % SiO₂,13-13.5 wt % Na₂O, 1-1.4 wt % Al₂O₃; 8.1-8.6 wt % CaO, and 4.5-5 wt %MgO.

The total iron in the glass composition may be in the range of 0.01 to0.60 wt %. The glass composition may have a redox ratio of less than orequal to 0.6. The glass composition may further comprise a colorantportion comprising CoO in an amount ranging from 30 to 120 ppm and/or Sein an amount no greater than 7.5 ppm. The glass composition may, whenformed as a glass sheet, have a color described by the followingchromaticity coordinates: an a* ranging from 4 to +4 and a b* rangingfrom 0 to 20. The glass composition may, when formed as a glass sheet,have a visible light transmittance of no greater than 80%.

The total iron in the glass composition may be in the range of 0.2 to0.8 wt %. The glass composition may have a redox ratio in the range of0.4-0.6. The glass composition may further comprise a colorant portioncomprising CoO in an amount no greater than 20 ppm and/or Se in anamount no greater than 3 ppm. The glass composition, when formed as aglass sheet, may have a color described by the following chromaticitycoordinates: an a* ranging from 8 to -16 and a b* ranging from +3 to−17. The glass composition may, when formed as a glass sheet, have avisible light transmittance of no greater than 80%.

The colorant portion may comprise at least one of the following: oxidesof manganese, tin, cerium, molybdenum, vanadium, copper, zinc, tungsten,and lanthanum, or any combination thereof.

These and other features and characteristics of the present invention,as well as the methods of operation and functions of the relatedelements of structures and the combination of parts and economies ofmanufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theincluded examples, all of which form a part of this specification. It isto be expressly understood, however, that the examples are for thepurpose of illustration and description only and are not intended as adefinition of the limits of the invention. As used in the specificationand the claims, the singular form of “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

All numbers used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. By “about” is meanta range of plus or minus ten percent of the stated value.

All ranges disclosed herein encompass the beginning and ending rangevalues and any and all subranges subsumed therein. The ranges disclosedherein represent the average values over the specified range.

All documents referred to herein are “incorporated by reference” intheir entirety.

By “at least” is meant “greater than or equal to”. By “not greater than”or “at most” is meant “less than or equal to”.

Any reference to amounts, unless otherwise specified, is “by wt %” (wt%).

The term “includes” is synonymous with “comprises”.

The discussion of the invention may describe certain features as being“particularly” or “preferably” within certain limitations (e.g.,“preferably”, “more preferably”, or “even more preferably”, withincertain limitations). It is to be understood that the invention is notlimited to these particular or preferred limitations but encompasses theentire scope of the disclosure.

As used herein, the term visible light transmittance (“Tvis”) representsa computed value based on measured transmittance data using CIE standardilluminate “D65” and CIE 1931 standard)(2° observer over the wavelengthrange of 380 to 770 nanometers at 10 nanometer intervals.

As used herein, color is described in terms of chromaticity coordinatesa* and b* which represent computed values based on measuredtransmittance data using CIE standard illuminate “D65” and CIE 1964supplementary standard (10°) observer. Transmitted data are collectedwith a Perkin-Elmer Lambda 9 spectrophotometer with a 150 mm Labsphereintegrating sphere lined with Spectralon, following the methodology ofASTM E903-96, “Standard Test Method for Solar Absorptance, Reflectance,and Transmittance of Materials using Integrating Spheres.”

Calculation of Tvis (also known as tristimulus value “Y”) andchromaticity coordinates follows the methodology found in ASTM E308-90,“Standard Test Method for Computing the Colors of Objects Using the CIESystem.”

Color values (e.g., L*, a*, b*, C*, and hue⁰) are in accordance with the1976 CIELAB color system specified by the International Commission onIllumination. The L*, a*, and b* values in the specification and claimsrepresent color center point values. As is standard practice in theindustry, all Tvis and chromaticity coordinates are determined using aflat glass sheet having a reference thickness of 5.66 mm (0.223 in).

Iron can be present in the glass composition as both ferric oxide(Fe₂O₃) and ferrous oxide (FeO). As is well known in the art, Fe₂O₃ is astrong absorber of ultraviolet radiation and is a yellow colorant, andFeO is a strong absorber of infrared radiation and is a blue colorant.The amount of iron present in the ferrous state (Fe⁺⁺) in the glasscomposition of the present invention is expressed in terms of the wt %of “FeO” present in the glass composition, as is standard practice inthe industry. As is appreciated by those skilled in the art, althoughthe amount of iron in the ferrous state (Fe⁺⁺) is expressed as FeO, theentire amount in the ferrous state (Fe⁺⁺) may not actually be present inthe glass as FeO.

The amount of “total iron” present in the glass composition of theinvention is expressed in terms of the wt % of “Fe₂O₃” present in theglass composition, as is standard practice in the industry. This doesnot imply that all of the iron present in the glass composition is inthe form of Fe₂O₃. As used herein, the term “redox ratio” indicates theamount of iron in the ferrous state (expressed as “FeO”) divided by theamount of total iron (expressed as “Fe₂O₃”).

The invention comprises, consists of, or consists essentially of thefollowing aspects of the invention, in any combination. Various aspectsof the invention are illustrated in separate examples. However, it is tobe understood that this is simply for ease of illustration anddiscussion. In the practice of the invention, one or more aspects of theinvention discussed in one example can be combined with one or moreaspects of the invention discussed in one or more of the other examples.

The invention relates to a glass composition including a base glassportion. In non-limiting embodiments the base glass portion is of thetype referred to in the art as a “soda-lime-silica” glass composition.In some non-limiting embodiments, the glass composition may furtherinclude a colorant portion, which includes colorants selected amounts toprovide a glass substrate or sheet formed from the glass compositionwith targeted optical properties, as described in further detail herein.For example, the colorant portion may comprise colorants including, butnot limited to, iron oxides (both ferric oxide (Fe₂O₃) and ferrous oxide(FeO)), cobalt oxide (CoO), selenium (Se), chromium oxide (Cr₂O₃),neodymium oxide (Nd₂O₃), titanium oxide (TiO₂), erbium oxide (Er₂O₃),and nickel oxide (NiO). Unless indicated otherwise, the wt % of acomponent of the base glass portion, and of the glass colorant portionof the glass composition is based on the total weight of the glasscomposition, i.e., the total weight of the base glass portion plus thetotal weight of the colorant portion.

In accordance with the present disclosure, it has been found that thechemical durability of a glass may be improved, and the targeted opticalcharacteristics (e.g., the color and light transmittances as describedherein) may be maintained or improved upon by providing a base glasscomposition as described herein. For example, in some non-limitingembodiments, the base glass portion may include 68-74 wt % SiO₂, morepreferably, 70-73 wt % SiO₂, more preferably, 71.75-72.25 wt % SiO₂, andmost preferably 71.762 to 71.905 wt % SiO₂. The base glass portion mayfurther include 8.1-8.6 wt % CaO, more preferably 8.2-8.5 wt % CaO, morepreferably, 8.3-8.4 wt % CaO, and most preferably, 8.335-8.355 wt % CaO.The base glass portion may further include 13-13.5 wt % Na₂O, preferably13.1-13.4 wt % Na₂O, more preferably 13.15-13.3 wt % Na₂O, and mostpreferably 13.19-13.25 wt % Na₂O. The base glass portion may furtherinclude 1-1.4 wt % Al₂O₃, more preferably 1.1-1.3 wt % Al₂O₃, morepreferably 1.15-1.25 wt % Al₂O₃, and most preferably, 1.21 to 1.23 wt %Al₂O₃. The base glass portion may further include 4.5-5 wt % MgO,preferably 4.6-4.9 wt % MgO, more preferably 4.7-4.8 wt % MgO, and mostpreferably 4.71-4.73 wt % MgO. The base glass portion may furtherinclude 0.1-0.5 wt % K₂O, preferably 0.2-0.4 wt % K₂O, more preferably0.30-0.35 wt % K₂O, and most preferably, 0.32-0.34 wt % K₂O. Inaddition, the base glass portion may contain non-effective trampmaterials such as SrO, ZrO₂, Cl and BaO, generally in concentrations ofless than 1 wt %.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include 71.99-72.11 wt % SiO₂, 8.10-8.26 wt % CaO,13.22-13.32 wt % Na₂O, 1.18-1.26 wt % Al₂O₃, 4.71-4.73 wt % MgO, and/or0.316-0.336 wt % K₂O.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include 71.69-71.75 wt % SiO₂, 8.06-8.14 wt % CaO,13.18-13.23 wt % Na₂O, 1.22-1.25 wt % Al₂O₃, 4.63-4.68 wt % MgO, and/or0.323-0.331 wt % K₂O.

In addition, in accordance with the present disclosure, it has beenfound that the chemical durability of a glass may be improved, and thetargeted optical characteristics (e.g., the color and lighttransmittances as described herein) may be maintained or improved uponby providing a base glass composition including a ratio of Na₂O to Al₂O₃in the range of 9.5-12.5 wt %/wt %, preferably, in the range of10.0-11.5 wt %/wt %, more preferably, in the range of 10.5-11.0 wt %/wt%, and most preferably, in the range of 10.55-10.90 wt %/wt %.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include a ratio of Na₂O to Al₂O₃ in the range of10.540-11.220 wt %/wt %.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include a ratio of Na₂O to Al₂O₃ in the range of10.552-10.884 wt %/wt %.

Further, in accordance with the present disclosure, it has been foundthat the chemical durability of a glass may be improved, and thetargeted optical characteristics (e.g., the color and lighttransmittances as described herein) maintained or improved upon byproviding a base glass composition including a ratio of CaO to MgO inthe range of 1.5-2.2 wt %/wt %, more preferably, in the range of 1.6-2.1wt %/wt %, more preferably, in the range of 1.65-1.85 wt %/wt %, andmost preferably, in the range of 1.7-1.8 wt %/wt %.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include a ratio of CaO to MgO in the range of1.76-1.80 wt %/wt %.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably include a ratio of CaO to MgO in the range of1.72-1.75 wt %/wt %.

Additionally, in accordance with the present disclosure, it has beenfound that providing a ratio of Na₂O to Al₂O₃ in the ranges discussedabove allows for the amount of K₂O to be increased as compared toexisting compositions while still maintaining or improving upon thetargeted optical characteristics (e.g., the color and lighttransmittances as described herein), such that the base glasscomposition may include K₂O in the ranges discussed above.

In some non-limiting embodiments, it may be desired that the glasscomposition, when formed as a glass sheet or substrate, meets certaincolor and light transmission requirements in accordance with a desiredapplication.

For example, in some non-limiting embodiments, it may be desired toproduce a glass sheet that has a color having the following chromaticitycoordinates: an a* ranging from −4 to +4 and a b* ranging from 0 to −20;preferably an a* ranging from -3 to +1 and a b* ranging from −2 to −12;more preferably ranging from an a* −2.5 to 0, and a b* ranging from −4to −9, and most preferably ranging from an a* −1.8 to −0.5 and a b* −5to −8. Glasses with these color coordinates are considered blue-violetin color. It may further be desirable that the glass sheet or substratemay also have a visible light transmittance (“Tvis”) of no greater than80%, preferably ranging from 40% to 80%, more preferably from 50% to76%, more preferably from 55% to 72%, and most preferably 58 to 70%.

In accordance with the present disclosure, it has been found that thiscan be achieved by providing a glass composition including a base glassportion as described herein and where the total iron in the glasscomposition is in the range of 0.01 to 0.60 wt %, preferably in therange of 0.08 to 0.26 wt %, more preferably in the range of 0.15 to 0.25wt %, and most preferably in the range of 0.16 to 0.17 wt %. The glasscomposition may have a redox ratio of less than or equal to 0.6,preferably in the range of 0.10-0.35, more preferably in the range of0.2 to 0.35, most preferably in the range of 0.20-0.31.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably have a total iron content in the range of0.155-0.210 wt % and a redox ratio in the range of 0.221-0.311.

In addition, the glass composition may be provided with a colorantportion including cobalt oxide (CoO), which is a blue colorant. Forexample, the colorant may include CoO in an amount ranging from 30 to120 parts per million (“ppm”), preferably in the range of 32 to 90 ppm,more preferably in the range of 45 to 60 ppm, and most preferably in therange of 37 to 50 ppm.

Alternatively, in some non-limiting embodiments, the colorant portionmay most preferably include CoO in an amount ranging from 49-57 ppm.

Additionally, the colorant portion may include Selenium (Se) in anamount no greater than 7.5 ppm, preferably from 1 to 6 ppm, morepreferably from 2 to 5.5 ppm and most preferably from 3 to 5 ppm. It isnoted that selenium can exist in glass in four oxidation states: Se⁺⁴and Se⁺², which add no color to the glass, Se⁰, which in the glass is apink colorant, and Se⁻², which in the presence of iron is a bronzecolorant. As is the standard practice in the industry, total selenium isexpressed as weight fraction of Se even though it may not be in theelemental state in the glass.

Alternatively, in some non-limiting embodiments, the colorant portionmay most preferably include Se in an amount ranging from 2 to 7 ppm.

In other non-limiting embodiments, it may be desired to produce a glasssubstrate or sheet that has the following chromaticity coordinates: ana* ranging from −8 to −16 and a b* ranging from +3 to −17; preferably ana* ranging from −11 to −13 and a b* ranging from −6 to −8; morepreferably an a* ranging from −11.5 to −12.5, and a b* ranging from −6.5to −7.5, and most preferably an a* ranging from −11.75 to −12.25 and ab* ranging from −6.75 to −7.25. It may further be desirable that theglass substrate or sheet have a Tvis of no greater than 80%, preferablyranging from 40% to 80%, more preferably from 60% to 75%, and mostpreferably from 66% to 70%.

In accordance with the present disclosure, it has been found that thiscan be achieved by providing a glass composition including a base glassportion as described herein and where the total iron in the glasscomposition is in the range of 0.2 to 0.8 wt %, preferably in the rangeof 0.3 to 0.7 wt %, more preferably in the range of 0.42 to 0.62 wt %,most preferably in the range of 0.46 to 0.58 wt %. In some non-limitingembodiments, the glass composition may have a redox ratio in the rangeof 0.4-0.6, preferably in the range of 0.47-0.60, more preferably in therange of 0.52 to 0.58, and most preferably in the range of 0.54 to 0.56.

Alternatively, in some non-limiting embodiments, the base glass portionmay most preferably have a total iron content in the range of 0.49-0.58wt % a redox ratio in the range of 0.47 to 0.54.

In addition, the glass composition may be provided with a colorantportion including CoO in an amount no greater than 20 ppm, preferably inthe range of 2 to 15 ppm, more preferably in the range of 4 to 12 ppm,and most preferably in the range of 6 to 10 ppm.

Alternatively, in some non-limiting embodiments, the colorant portionmay most preferably include CoO in an amount ranging from 7.1-12.1 ppm.

Additionally, the colorant portion may include Se in an amount nogreater than 3 ppm, preferably in the range of 0.25 to 2 ppm, and mostpreferably in the range of 0.5 to 1.75 ppm.

Alternatively, in some non-limiting embodiments, the colorant portionmay most preferably include Se in an amount no greater than 3 ppm.

It will be appreciated by those skilled in the art that a glasscomposition in accordance with the present invention is not limited tothe above-described combinations of colorants and the amounts thereof.For example, it has been found that as the ratio of CoO to Se increasesand the amount of the other colorants in the glass composition remainconstant, the color of the glass is more blue, and as the ratio of CoOto Se decreases and the amount of the other colorants in the glasscomposition remain constant, the color of the glass is less blue andmore yellow. Accordingly, in some non-limiting embodiments, the glasscomposition of the present invention may have a wt % ratio of CoO to Seequal to or greater than 5, more preferably, in a range of 7 to 18, andmost preferably in a range of 10 to 13. Alternatively, in furthernon-limiting embodiments, the wt % ratio of CoO to Se may be preferablyat least 6, more preferably at least 7, and most preferably at least 8.

In addition, in non-limiting embodiments, certain types of colorants maybe substituted for other colorants while still achieving acceptableresults. For example, it has been found that the glass colorant portioncan include a mixture of chromium oxide and cobalt oxide to reduce thewt % of iron oxide while still achieving acceptable for results. Forexample, and not limiting to the invention, a mixture of 6 ppm Cr₂O₃ and0.4 ppm CoO can be added to compensate for a reduction of 100 ppm ofFe₂O₃, while still achieving acceptable optical characteristics.

Similarly, in some non-limiting embodiments, neodymium oxide, a bluecolorant, can be included in the composition to reduce the wt % ofcobalt oxide. For example, and not limiting to the invention, 180 ppmneodymium oxide expressed as Nd₂O₃ can be added to compensate for every1 ppm reduction of CoO, while still achieving acceptable opticalcharacteristics. For example, in non-limiting embodiments, a glasscomposition including 180 ppm neodymium oxide may have a colorantportion including CoO in an amount no greater than 19 ppm, preferably inthe range of 1 to 14 ppm, more preferably in the range of 3 to 11 ppm,and most preferably in the range of 5 to 9 ppm.

Similarly, in another non-limiting embodiment of the invention, amixture of 4000 ppm erbium oxide as Er₂O₃, a pink colorant, and 1200 ppmFe2O3 can replace a mixture of 1 ppm Se and 6 ppm CoO. Furthermore, amixture of 1600 ppm titanium oxide as TiO₂, a yellow colorant, and 4 ppmCoO can replace a mixture of 1 ppm Se and 600 ppm Fe₂O₃.

Other colorants that can be used in the practice of the inventioninclude but are not limited to oxides of manganese, tin, cerium,molybdenum, vanadium, copper, zinc, tungsten and lanthanum. For example,in one non-limiting embodiment, 1000 ppm of MnO₂, a yellow colorant inglass, can replace a mixture of 1 ppm Se and 200 ppm Fe₂O₃, while stillachieving acceptable optical characteristics.

Although not limiting to the invention, in the preferred practice of theinvention nickel oxide is excluded from the glass composition because ofthe tendency to form nickel sulfide stone defects, which can causespontaneous breakage in tempered glass. However, in those instances whenenvironmental concerns restrict the use of selenium, nickel oxide,titanium oxide, and also erbium oxide, an expensive glass colorant, canbe used to reduce the wt % of selenium. For example, and not limiting tothe invention, a mixture of 35 ppm nickel oxide as NiO, a yellowcolorant in glass, and 1 ppm of CoO can replace a mixture of 1 ppm of Seand 700 ppm Fe₂O₃.

In a non-limiting embodiment of the invention, the described glasscomposition is formed into a glass substrate using any conventionalglass making process known in the art, and preferably using a continuousflat glass making process. For example, but not limiting to theinvention, the glass composition can be formed from batch materials viacrucible melts, a sheet drawing process, a float glass process, etc. Forexample, in some non-limiting embodiments, the described glasscomposition may be formed by a process including the following steps:feeding raw materials as batch materials to a container (e.g., acrucible), melting the batch materials in the container to form a moltenglass composition, passing, from the container, the molten glasscomposition into a pool of a molten metal (e.g., tin) such that themolten glass composition floats in the pool of molten metal, forming themolten glass composition into the shape of a flat glass product on thepool of molten metal, and cooling the molten glass composition to form aflat glass product. In the preferred practice of the invention, theglass is melted and refined in a continuous, large-scale, commercialglass melting operation and formed into flat glass sheets of varyingthickness, e.g., but not limiting to the invention up to 25 millimeters(“mm”) by the float process in which the molten glass is supported on apool of molten metal, usually tin, as it assumes a ribbon shape and iscooled, in a manner well known in the art.

In some non-limiting embodiments, the glass compositions describedherein may be obtained by using one or more of the following rawmaterials as batch materials: Nepheline Syenite, limestone, dolomite,soda ash, rouge, graphite, salt cake, alumina, and cullet (i.e.,recycled glass).

Although it is preferred that the glass described herein be made using aconventional, overhead fired continuous melting operation, as is wellknown in the art, the glass can also be produced using a multi-stagemelting operation, as described in U.S. Pat. Nos. 4,381,934 to Kunkle,et al., 4,792,536 to Pecoraro, et al. and 4,886,539 to Cerutti, et al.If required, a stirring arrangement can be employed within the meltingand/or forming stages of the glass production operation to homogenizethe glass in order to improve the optical quality of the glass.

Depending on the type of melting operation, sulfur can be added to thebatch materials of a soda-lime-silica glass as a melting and refiningaid. Commercially produced float glass can include up to about 0.3 wt %SO₃. In a glass composition that includes iron and sulfur, providingreducing conditions can create amber coloration which lowers luminoustransmittance as discussed in U.S. Pat. No. 4,792,536 to Pecoraro, etal. However, it is believed that the reducing conditions required toproduce this coloration in float glass compositions of the typedescribed herein are limited to approximately the first 20 microns ofthe lower glass surface contacting the molten tin during the floatforming operation, and to a lesser extent, to the exposed upper glasssurface. Because of the glass low sulfur content and the limited regionof the glass in which any coloration could occur, depending on theparticular soda-lime-silica glass composition, sulfur in these surfacesessentially has no material effect on the glass color or spectralproperties.

It should be appreciated that as a result of forming the glass on moltentin as discussed above, measurable amounts of tin oxide may migrate intosurface portions of the glass on the side contacting the molten tin.Typically, a piece of float glass has an SnO₂ concentration ranging fromabout 0.05 to 2 wt % in about the first 25 microns below the surface ofthe glass that was in contact with the tin. Typical background levels ofSnO₂ can be as high as 30 ppm. It is believed that high tinconcentrations in about the first 10 angstroms of the glass surfacesupported by the molten tin can slightly increase the reflectivity ofthat glass surface; however, the overall impact on the glass propertiesis minimal.

As is appreciated by those skilled in the art of glass making, a resultof the raw materials and/or equipment used to produce glass, includingproducing glass of the present invention, results in certain impurities,for example, SrO and ZrO₂, being present in the final glass composition.Such materials are present in the glass composition in minor amounts andare referred to herein as “tramp materials”. By way of illustration andnot limiting to the invention, it is believed that glass compositions ofthe instant invention produced by a commercial float process asdiscussed earlier can include low concentrations, e.g., tramp levels ofcolorants, e.g., Cr₂O₃, MnO₂ and TiO₂. These levels are referred to as“tramp levels” because they do not materially affect the colorcharacteristics and spectral properties of glass sheets or substratesformed from the glass compositions of the invention. For example, andnot limiting to the invention, Cr₂O₃ in amounts no greater than 10 ppmis considered a tramp material; MnO₂ in amounts no greater than 50 ppmis considered a tramp material, and TiO₂ in amounts no greater than 0.02wt % is considered a tramp material.

In view of the foregoing and as illustrated by the following examples,it can now be appreciated by those skilled in the art, glass substrateshaving 1-1.4 wt % Al₂O₃, preferably, 1.1-1.3 wt % Al₂O₃, morepreferably, 1.15-1.25 wt % Al₂O₃, and most preferably, 1.21 to 1.23 wt %Al₂O₃; and 13-13.5 wt % Na₂O, preferably, 13.1-13.4 wt % Na₂O, morepreferably, 13.15-13.3 wt % Na₂O, and most preferably, 13.19-13.25 wt %Na₂O show markedly improved durability. Further, it may now beappreciated that glass substrates where the ratio of Na₂O to Al₂O₃ is inthe range of 9.5-12.5 wt %/wt %, preferably, in the range of 10.0-11.5wt %/wt %, more preferably, in the range of 10.5-11.0 wt %/wt %, andmost preferably, in the range of 10.55-10.90 wt %/wt %, show markedlyimproved durability over as compared to other glass compositions, suchas those having a higher Na₂O concentration and a lower Al₂O₃concentration.

In addition, in view of the foregoing and as illustrated by thefollowing examples, it may now be appreciated that glass substrateshaving 8.1-8.6 wt % CaO, preferably 8.2-8.5 wt % CaO, more preferably,8.3-8.4 wt % CaO, and most preferably, 8.335-8.355 wt % CaO; and 4.5-5wt % MgO, preferably 4.6-4.9 wt % MgO, more preferably 4.7-4.8 wt % MgO,and most preferably, 4.71-4.73 wt % MgO, show markedly improveddurability. Further, it may now be appreciated that glass substrateswhere the ratio of CaO to MgO is in the range of 1.5-12.2 wt %/wt %,preferably, in the range of 1.6-2.1 wt %/wt %, more preferably, in therange of 1.65-1.85 wt %/wt %, and most preferably, in the range of1.70-1.80 wt %/wt %, show markedly improved chemical durability overother glass compositions, such as those having a higher CaOconcentration and a lower MgO concentration.

In addition, in view of the foregoing and as illustrated by thefollowing examples, it may now be appreciated that glass substrateshaving 0.1-0.5 wt % K₂O, preferably, 0.2-0.4 wt % K₂O, more preferably,0.30-0.35 wt % K₂O, and most preferably, 0.32-0.34 wt % K₂O showmarkedly improved chemical durability over other glass compositions,such as those having a lower K₂O concentration.

In certain embodiments, the glass substrates or glass compositions cancontain the constituents identified in Table 1, below.

TABLE 1 A B C D E Comp wt. % wt. % wt. % wt. % wt. % SiO₂ 71.7-72.071.2-71.6 71.4-72.0 71.9-72.2 71.6-71.8 Na₂O 13.1-13.3 13.4-13.513.1-13.4 13.2-13.4 13.1-13.3 K₂O 0.24-0.33 0.24-0.25 0.29-0.310.32-0.34 0.32-0.33 CaO 8.3-8.4 8.3-8.6 8.2-8.6 8.0-8.3 8.0-8.2 MgO4.7-4.8 5.0-5.2 4.6-5.0 4.5-4.7 4.6-4.7 Al₂O₃ 1.2-1.3 1.1-1.2 1.1-1.31.1-1.3 1.2-1.3 Fe₂O₃ 0.16-0.17 0.20-0.21 0.16-0.17 0.16-0.18 0.49-0.58Comp wt. %/ wt. %/ wt. %/ wt. %/ wt. %/ Ratios wt. % wt. % wt. % wt. %wt. % Na₂O:Al₂O₃ 10.7-11.0 11.1-11.3 10.5-11.4, 10.4-11.2 10.5-10.9 morepreferably 10.5-11.3, most preferably 10.6-11.2 CaO:MgO 1.7-2.9 1.7-1.9,1.6-1.9, 1.7-1.9 1.7-1.8 most more preferably preferably 1.7-1.81.7-1.8, most preferably 1.72-1.76

Optionally, Composition D from Table 1 may include a colorant. Thecolorant may include CoO; SeO; Cr₂O₃; and/or MnO₂ in the amountsdescribed above. Optionally, Composition E from Table 1 may include acolorant. The colorant may CoO; Cr₂O₃; and/or MnO₂ in the amountsdescribed above.

EXAMPLES

Non-limiting embodiments of the present invention are illustrated by thefollowing non-limiting examples. Comparative Examples C1-C5, shown inTable 1, and Examples 1-10, shown in Tables 2 and 3, were made using acontinuous flat glass making process, as described herein, and the finalcomposition of each sample was determined by X-Ray FluorescenceSpectroscopy.

The chemical durability shown for each example represents a measurementof the hydrolytic resistance of the glass and was calculated by theprocedures described in the International Organization forStandardization test ISO 719, which is available at:<https://www.iso.org/standard/4948.html>, and which is herebyincorporated by reference in its entirety herein. In accordance with ISO719, 2g of each glass sample, particle size 300-500 μm, was kept for 60min in 50 mL deionized water of grade 2 at 98 degrees C. 25 mL of theobtained solution was then titrated against 0.01 mol/L HCl solution tothe point of neutralization. The volume of the HCl needed forneutralization was then used to determine the amount of Na₂O that wasextracted from the glass. The values shown in the Durability rows ofTables 1, 2, and 3, represent the amount of Na₂O that was extracted inμm, with lower values representing an improved chemical durability.

Table 1, below shows data for comparative examples, C1-C5.

Example C1 C2 C3 C4 C5 SiO₂ 72.92 71.375 71.49 71.395 71.365 Na₂O 13.7213.125 13.115 13.46 13.455 K₂O 0.085 0.0625 0.062 0.2445 0.243 CaO 8.849.215 9.145 8.43 8.66 MgO 3.83 4.18 4.14 5.09 4.9 Al₂O₃ 0.16 0.98 0.980.96 0.96 SO₃ 0.156 0.1595 0.1655 0.177 0.176 Fe₂O₃ 0.168 0.8726 0.870450.20105 0.2003 Cl 0 0.012 0.0115 0.014 0.013 Cr₂O₃ 0.0002 0.0003350.00033 0.000295 0.00031 MnO₂ 0.0054 0.0076 0.00905 0.00635 0.00625 TiO₂0.012 0.01 0.01 0.01 0.01 ZnO 0.041 0.001 0.001 0.001 0.001 Na₂O/Al₂O₃85.75 13.39286 13.38265 14.02083 14.01563 CaO/MgO 2.308094 2.2045452.208937 1.656189 1.767347 Durability 253 202 202 200 204

Table 2, below, shows data for examples 1-5

TABLE 2 Example 1 2 3 4 5 SiO₂ 71.845 71.77 71.905 71.715 71.635 Na₂O13.22 13.24 13.225 13.245 13.18 K₂O 0.294 0.2965 0.2965 0.296 0.305 CaO8.32 8.345 8.285 8.395 8.48 MgO 4.755 4.79 4.725 4.81 4.8 Al₂O₃ 1.211.21 1.22 1.195 1.245 SO₃ 0.1615 0.156 0.1595 0.1485 0.1625 Fe₂O₃ 0.16390.16375 0.163 0.1631 0.16195 Cl 0.013 0.0115 0.012 0.013 0.0125 Cr₂O₃0.00018 0.00026 0.00018 0.00017 0.0002 MnO₂ 0.00625 0.0063 0.0062 0.00620.0062 TiO₂ 0.0105 0.01 0.01 0.01 0.01 ZnO 0.001 0.001 0.001 0.001 0.001Na₂O/Al₂O₃ 10.92562 10.94215 10.84016 11.08368 10.586345 CaO/MgO1.749737 1.742171 1.753439 1.745322 1.7666667 Durability 183 183 183 182182

Table 3, below is a continuation of Table 2, and shows data for examples6-10

TABLE 3 Example 6 7 8 9 10 SiO₂ 71.98 71.42 71.675 71.875 71.615 Na₂O13.245 13.32 13.275 13.11 13.25 K₂O 0.291 0.296 0.2965 0.2985 0.297 CaO8.255 8.505 8.43 8.38 8.485 MgO 4.695 4.92 4.765 4.745 4.785 Al₂O₃ 1.1751.195 1.21 1.23 1.22 SO₃ 0.156 0.1445 0.1485 0.152 0.1625 Fe₂O₃ 0.16540.16675 0.16485 0.1665 0.16415 Cl 0.014 0.0135 0.013 0.014 0.0135 Cr₂O₃0.000245 0.000245 0.00022 0.00019 0.000305 MnO₂ 0.00615 0.0061 0.006250.00615 0.00615 TiO₂ 0.01 0.01 0.01 0.0105 0.0095 ZnO 0.001 0.001 0.0010.001 0.001 Na₂O/Al₂O₃ 11.2723404 11.14644 10.97107 10.658537 10.860656CaO/MgO 1.75825346 1.728659 1.76915 1.7660695 1.7732497 Durability 184184 184 178 185

The invention is described further in the following numbered clauses:

Clause 1. A glass composition comprising a base glass portioncomprising: 65-75 wt % SiO₂; 5-15 wt % CaO; 0-5 wt % MgO; 0-5 wt % K₂O;10-14 wt % Na₂O; and 1-5 wt % Al₂O₃; wherein the glass composition has aratio of Na₂O to Al₂O₃ is in the range of 9.5-12.5 wt %/wt %, preferablyin the range of 10.0-11.5 wt %/wt %, more preferably in the range of10.5-11.0 wt %/wt %, and most preferably in the range of 10.55-10.90 wt%/wt %.

Clause 2. The glass composition of clause 1, wherein: the base glassportion has a ratio of CaO to MgO in the range of 1.5-2.2 wt %/wt %,preferably, in the range of 1.6-2.1 wt %/wt %, more preferably, in therange of 1.65-1.85 wt %/wt %, and most preferably, in the range of1.7-1.8 wt %/wt %.

Clause 3. The glass composition of any one of clauses 1-2, wherein: thebase glass portion comprises 0.1-0.5 wt % K₂O, preferably 0.2-0.4 wt %K₂O, more preferably 0.30-0.35 wt % K₂O, and most preferably 0.32-0.34wt % K₂O.

Clause 4. The glass composition of any one of the preceding clauses,wherein the base glass portion comprises: 68-74 wt % SiO₂, morepreferably, 70-73 wt % SiO₂, more preferably, 71.75-72.25 wt % SiO₂, andmost preferably 71.7 to 72 wt % SiO₂, 13-13.5 wt % Na₂O, preferably13.1-13.4 wt % Na₂O, more preferably 13.15-13.3 wt % Na₂O, and mostpreferably, 13.1-13.7 wt % Na₂O; 1-1.4 wt % Al₂O₃, more preferably1.1-1.3 wt % Al₂O₃, more preferably 1.15-1.25 wt % Al₂O₃, and mostpreferably 1.21 to 1.23 wt % Al₂O₃; 8.0-8.6 wt % CaO, preferably 8.2-8.5wt % CaO, more preferably, 8.3-8.4 wt % CaO, and most preferably, 8.335to 8.355 wt % CaO; and/or 4.5-5 wt % MgO, preferably 4.6-4.9 wt % MgO,more preferably 4.7-4.8 wt % MgO, and most preferably, 4.71 to 4.73 wt %MgO.

Clause 5. The glass composition of any one of the preceding clauses,wherein the total iron in the glass composition is in the range of 0.01to 0.30 wt %, preferably in the range of 0.04 to 0.28 wt %, morepreferably in the range of 0.08 to 0.26 wt %, more preferably in therange of 0.15 to 0.25 wt %, and most preferably in the range of 0.163 to0.165 wt %.

Clause 6. The glass composition of any one of the preceding clauses,wherein the glass composition has a redox ratio of less than or equal to0.6, preferably in the range of 0.10-0.35, and most preferably in therange of 0.2 to 0.31.

Clause 7. The glass composition of any one of the preceding clauses,further comprising a colorant portion, the colorant portion comprising:CoO in an amount ranging from 30 to 120 ppm, preferably in the range of32 to 90 ppm, more preferably in the range of 45 to 60 ppm, and mostpreferably in the range of 37 to 50 ppm; and/or Se in an amount nogreater than 7.5 ppm, preferably in the range of 1 to 6 ppm, morepreferably in the range of 2 to 5.5 ppm, and most preferably in therange of 3 to 5 ppm.

Clause 8. The glass composition of any one of the preceding clauses,wherein the glass composition, when formed as a glass sheet, has a colordescribed by the following chromaticity coordinates: an a* ranging from−4 to +4 and a b* ranging from 0 to −20; preferably an a* ranging from−3 to +1 and a b* ranging from −2 to −12; more preferably ranging froman a* −2.5 to 0, and a b* ranging from −4 to −9, and most preferablyranging from an a* −1.8 to −0.5 and a b* −5 to −8.

Clause 9. The glass composition of any one of the preceding clauses,wherein the glass composition, when formed as a glass sheet, has avisible light transmittance ranging from no greater than 80%, preferably40% to 80%, more preferably from 50% to 76%, more preferably from 55% to72%, and most preferably 58 to 70%.

Clause 10. The glass composition of any one of clauses 1-4, wherein thetotal iron in the glass composition is in the range of 0.2 to 0.8 wt %,preferably in the range of 0.3 to 0.7 wt %, preferably in the range of0.42 to 0.62 wt %, preferably in the range of 0.46 to 0.58 wt %.

Clause 11. The glass composition of any one of clauses 1-4 and 10,wherein the glass composition has a redox ratio in the range of 0.4-0.6,preferably in the range of 0.47-0.60, more preferably in the range of0.52 to 0.58, and most preferably in the range of 0.54 to 0.56.

Clause 12. The glass composition of any one of clauses 1-4 and 10-11,further comprising a colorant portion comprising: CoO in an amount nogreater than 20 ppm, preferably in the range of 2 to 15 ppm, morepreferably in the range of 4 to 12 ppm, and most preferably in the rangeof 6 to 10 ppm; and/or Se in an amount no greater than 3 ppm, preferablyin the range of 0.25 to 2 ppm, and most preferably in the range of 0.5to 1.75 ppm.

Clause 13. The glass composition of any one of clauses 1-4 and 10-12,wherein the glass composition, when formed as a glass sheet has a colordescribed by the following chromaticity coordinates: an a* ranging from−8 to −16 and a b* ranging from +3 to −17; preferably an a* ranging from−11 to −13 and a b* ranging from −6 to −8; more preferably an a* rangingfrom −11.5 to −12.5, and a b* ranging from −6.5 to −7.5, and mostpreferably an a* ranging from −11.75 to −12.25 and a b* ranging from−6.75 to −7.25.

Clause 14. The glass composition of any one of clauses 1-4 and 10-13,wherein the glass composition, when formed as a glass sheet, has avisible light transmittance ranging from no greater than 80%, preferably40% to 80%, more preferably from 60% to 75%, and most preferably from66% to 70%.

Clause 15. The glass composition of any one of the preceding clauses,wherein the colorant portion comprises at least one of the following:oxides of manganese, tin, cerium, molybdenum, vanadium, copper, zinc,tungsten, and lanthanum, or any combination thereof.

Clause 16. A method of producing a glass sheet having: a color describedby the following chromaticity coordinates: an a* ranging from −4 to +4and a b* ranging from 0 to -20; preferably an a* ranging from −3 to +1and a b* ranging from −2 to −12; more preferably an a* ranging from −2.5to 0, and a b* ranging from −4 to −9, and most preferably an a* rangingfrom −1.8 to −0.5 and a b* ranging from −5 to −8; and a visible lighttransmittance of no greater than 80%, preferably ranging from 40% to80%, more preferably from 50% to 76%, more preferably from 55% to 72%,and most preferably 58 to 70%, the method comprising: producing, by afloat glass process, the glass composition according to any one ofclauses 1-7 and 15.

Clause 17. A method of producing a glass sheet having: a color describedby the following chromaticity coordinates: an a* ranging from −8 to −16and a b* ranging from +3 to −17; preferably an a* ranging from −11 to−13 and a b* ranging from −6 to −8; more preferably an a* ranging from−11.5 to −12.5, and a b* ranging from −6.5 to −7.5, and most preferablyan a* ranging from −11.75 to −12.25 and a b* ranging from −6.75 to−7.25; and a visible light transmittance of no greater than 80%,preferably ranging from 40% to 80%, more preferably from 60% to 75%, andmost preferably from 66% to 70%, the method comprising: preparing, by afloat glass process, a glass composition according to any one of clauses1-4, 11-12, and 15.

Clause 18. A method of producing a glass sheet having: a color describedby the following chromaticity coordinates: an a* ranging from −4 to +4and a b* ranging from 0 to −20; preferably an a* ranging from −3 to +1and a b* ranging from −2 to −12; more preferably an a* ranging from −2.5to 0, and a b* ranging from −4 to −9, and most preferably an a* rangingfrom −1.8 to −0.5 and a b* ranging from −5 to −8; and a visible lighttransmittance of no greater than 80%, preferably ranging from 40% to80%, more preferably from 50% to 76%, more preferably from 55% to 72%,and most preferably 58 to 70%, the method comprising: feeding rawmaterials as batch materials to a container melting the batch materialsin the container to form a glass composition according to any one ofclauses 1-7 and 15, passing, from the container, the molten glasscomposition into a pool of a molten metal, preferably tin, such that themolten glass composition floats in the pool of molten metal, forming themolten glass composition into the shape of the flat glass sheet on thepool of molten metal, and cooling the molten glass composition to formthe flat glass sheet.

Clause 19. A method of producing a glass sheet having: a color describedby the following chromaticity coordinates: an a* ranging from −8 to −16and a b* ranging from +3 to −17; preferably an a* ranging from −11 to−13 and a b* ranging from −6 to −8; more preferably an a* ranging from−11.5 to −12.5, and a b* ranging from −6.5 to −7.5, and most preferablyan a* ranging from −11.75 to −12.25 and a b* ranging from −6.75 to−7.25; and a visible light transmittance of no greater than 80%,preferably ranging from 40% to 80%, more preferably from 60% to 75%, andmost preferably from 66% to 70%, the method comprising: feeding rawmaterials as batch materials to a container, melting the batch materialsin the container to form a glass composition according to any one ofclauses 1-4, 11-12, and 15, passing, from the container, the moltenglass composition into a pool of a molten metal, preferably tin, suchthat the molten glass composition floats in the pool of molten metal,forming the molten glass composition into the shape of the flat glasssheet on the pool of molten metal, and cooling the molten glasscomposition to form the flat glass sheet.

Clause 20. The method of any one of clauses 19 and 20, wherein the batchmaterials comprise at least one of the following: Nepheline Syenite,limestone, dolomite, soda ash, rouge, graphite, salt cake, alumina, andcullet, or any combination thereof.

Clause 21. Use of a glass composition according to any one of clauses1-7 and 15 in a float glass process to form a glass sheet having: acolor described by the following chromaticity coordinates: an a* rangingfrom −4 to +4 and a b* ranging from 0 to −20; preferably an a* rangingfrom −3 to +1 and a b* ranging from −2 to −12; more preferably an a*ranging from −2.5 to 0, and a b* ranging from −4 to −9, and mostpreferably an a* ranging from −1.8 to −0.5 and a b* ranging from −5 to−8; and a visible light transmittance of no greater than 80%, preferablyranging from 40% to 80%, more preferably from 50% to 76%, morepreferably from 55% to 72%, and most preferably 58 to 70%.

Clause 22. Use of a glass composition according to any one of clauses1-4, 11-12, and 15 in a float glass process to form a glass sheethaving: an a* ranging from −8 to −16 and a b* ranging from +3 to −17;preferably an a* ranging from −11 to −13 and a b* ranging from −6 to −8;more preferably an a* ranging from −11.5 to −12.5, and a b* ranging from−6.5 to −7.5, and most preferably an a* ranging from −11.75 to −12.25and a b* ranging from −6.75 to −7.25; and a visible light transmittanceof no greater than 80%, preferably ranging from 40% to 80%, morepreferably from 60% to 75%, and most preferably from 66% to 70%.

Clause 23. A glass composition comprising a base glass portioncomprising:

-   -   SiO₂ 71.7-72.0 wt. %;    -   CaO 8.3-8.4 wt. %;    -   MgO 4.7-4.8 wt. %;    -   K₂O 0.24-0.33 wt. %;    -   Na₂O 13.1-13.3 wt. %; and    -   Al₂O₃ 1.2-1.3 wt. %.

Clause 24. The glass composition of clause 23 further comprising0.16-0.17 wt. % Fe₂O₃.

Clause 25. The glass composition of clause 23 or clause 24 wherein theratio of Na₂O to Al₂O₃ is 10.7 11.0 wt. %/wt. %.

Clause 26. The glass composition of any one of clause 23-25 wherein theratio of CaO to MgO is 1.7-2.9 wt. %/wt %.

Clause 27. The glass composition of any one of clause 23-26 wherein thethe ratio of CaO to MgO is 1.7-1.9 wt. %/wt %.

Clause 28. The glass composition of any one of clause 23-26 wherein thethe ratio of CaO to MgO is 1.6-1.9 wt. %/wt %.

Clause 29. The glass composition of any one of clause 23-26 wherein thethe ratio of CaO to MgO is 1.7-1.8 wt. %/wt. %.

Clause 30. A glass composition comprising a base glass portioncomprising:

-   -   SiO₂ 71.2-71.6 wt. %;    -   CaO 8.3-8.6 wt. %;    -   MgO 5.0-5.2 wt. %;    -   K₂O 0.24-0.25 wt. %;    -   Na2O 13.4-13.5 wt. %; and    -   Al₂O₃ 1.1-1.2 wt. %.

Clause 31. The glass composition of clause 30 further comprising0.20-0.21 wt. % Fe₂O₃.

Clause 32. The glass composition of clause 30 or clause 31 wherein theratio of Na₂O to Al₂O₃ is 11.1 11.3 wt. %/wt %.

Clause 33. The glass composition of any one of clause 30-32 wherein theratio of CaO to MgO is 1.7-1.9 wt. %/wt. %.

Clause 34. The glass composition of any one of clause 30-33 wherein theratio of CaO to MgO is 1.7-1.8 wt. %/wt. %.

Clause 35. The glass composition of any one of clause 30-33 whereinthere is 8.3-8.4 wt. % of the CaO.

Clause 36. A glass composition comprising a base glass portioncomprising:

-   -   SiO₂ 71.4-72.0 wt. %;    -   CaO 8.2-8.6 wt. %;    -   MgO 4.6-5.0 wt. %;    -   K₂O 0.29-0.31 wt. %;    -   Na₂O 13.1-13.4 wt. %/wt %; and    -   Al₂O₃1.1-1.3 wt. %.

Clause 37. The glass composition of clause 36 further comprising0.16-0.17 wt. % Fe₂O₃.

Clause 38. The glass composition of clause 36 or clause 37 wherein theratio of Na₂O to Al₂O₃ is 10.5 11.4 wt. %/wt %.

Clause 39. The glass composition of any one of clause 36-38 wherein theratio of CaO to MgO is 1.6-1.9 wt. %/wt. %.

Clause 40. The glass composition of any one of clause 36-39 wherein theratio of Na₂O to Al₂O₃ is 10.5 11.3 wt. %/wt. %.

Clause 41. The glass composition of any one of clause 36-40 wherein theratio of Na₂O to Al₂O₃ is 10.6 11.2 wt. %/wt. %.

Clause 42. The glass composition of any one of clause 36-41 wherein theratio of CaO to MgO is 1.7 1.8 wt. %/wt. %.

Clause 43. A glass composition comprising a base glass portioncomprising:

-   -   SiO₂ 71.9-72.2 wt. %;    -   CaO 8.0-8.3 wt. %;    -   MgO 4.5-4.7 wt. %;    -   K₂O 0.32-0.34 wt. %;    -   Na₂O 13.2-13.4 wt. %; and    -   Al₂O₃ 1.1-1.3 wt. %.

Clause 44. The glass composition of clause 43 further comprising0.16-0.18 wt. % Fe₂O₃.

Clause 45. The glass composition of clause 43 or clause 44 wherein theratio of Na₂O to Al₂O₃ is 10.4 11.2 wt. %/wt. %.

Clause 46. The glass composition of any one of clause 43-45 wherein theratio of CaO to MgO is 1.7-1.9 wt. %/wt. %.

Clause 47. The glass composition of any one of clause 43-46 wherein theratio of Na₂O to Al₂O₃ is 10.5-10.9 wt. %/wt. %.

Clause 48. The glass composition of any one of clause 43-47 wherein theratio of Na₂O to Al₂O₃ is 10.7-11.0 wt. %/wt. %.

Clause 49. The glass composition of any one of the clauses 43-50 furthercomprising a colorant, wherein the colorant comprises CoO in a range of0.004 wt. % to 0.006 wt. %.

Clause 50. The glass composition of any one of the clauses 43-49 furthercomprising a colorant, wherein the colorant comprises Se in a range of0.0003 wt. % to 0.0007 wt. %.

Clause 51. The glass composition of any one of the clauses 43-50 furthercomprising a colorant, wherein the colorant comprises Cr₂O₃ in a rangeof 0.0002 wt. % to 0.0005 wt. %.

Clause 52. The glass composition of any one of the clauses 43-51 furthercomprising a colorant, wherein the colorant comprises MnO₂ in a range of0.005 wt. % to 0.007 wt. %.

Clause 53. The glass composition of any one of the clauses 43-52 furthercomprising a redox between 0.22 and 0.25.

Clause 54. A glass composition comprising a base glass portioncomprising:

-   -   SiO₂ 71.6-71.8 wt. %;    -   CaO 8.0-8.2 wt. %;    -   MgO 4.6-4.7 wt. %;    -   K₂O 0.32-0.33 wt. %;    -   Na₂O 13.1-13.3 wt. %/wt. %; and    -   Al₂O₃ 1.2-1.3 wt. %.

Clause 55. The glass composition of clause 54 further comprising 0.4-0.6wt. % Fe₂O₃, preferably 0.49-0.58 wt. % Fe₂O₃.

Clause 56. The glass composition of clause 54 or clause 55 wherein theratio of Na₂O to Al₂O₃ is 10.5 10.9 wt. %/wt. %.

Clause 57. The glass composition of any one of clause 54-56 wherein theratio of CaO to MgO is 1.7-1.8 wt. %/wt. %.

Clause 58. The glass composition of any one of the clauses 54-57 furthercomprising a colorant, wherein the colorant comprises CoO in a range of0.0007 wt. % to 0.002 wt. %.

Clause 59. The glass composition of any one of the clauses 54-58 furthercomprising a colorant, wherein the colorant comprises Cr₂O₃ in a rangeof 0.0003 wt. % to 0.0005 wt. %.

Clause 60. The glass composition of any one of the clauses 54-59 furthercomprising a colorant, wherein the colorant comprises MnO₂ in a range of0.005 wt. % to 0.007 wt. %.

Clause 61. The glass composition of any one of the clauses 54-60 furthercomprising a redox between 0.47 and 0.54.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

What is claimed is:
 1. A glass composition comprising a base glassportion comprising: 65-75 wt % SiO₂; 5-15 wt % CaO; 0-5 wt % MgO; 0-5 wt% K₂O; 10-14 wt % Na₂O; and 1-5 wt % Al₂O₃; wherein the glasscomposition has a ratio of Na₂O to Al₂O₃ is in the range of 9.5-12.5 wt%/wt %.
 2. The glass composition of claim 1, wherein the base glassportion has a ratio of CaO to MgO in the range of 1.5-2.2 wt %/wt %. 3.The glass composition of claim 1, wherein the base glass portioncomprises 0.1-0.5 wt % K₂O.
 4. The glass composition of claim 1, whereinthe base glass portion comprises: 68-74 wt % SiO₂; 13-13.5 wt % Na₂O;1-1.4 wt % Al₂O₃; 8.1-8.6 wt % CaO; and 4.5-5 wt % MgO.
 5. The glasscomposition of claim 1, wherein the total iron in the glass compositionis in the range of 0.01 to 0.30 wt %.
 6. The glass composition of claim1, further comprising a colorant portion, the colorant portioncomprising: CoO in an amount ranging from 30 to 120 ppm; or Se in anamount no greater than 7.5 ppm.
 7. The glass composition of claim 1,wherein the glass composition, when formed as a glass sheet, has a colordescribed by the following chromaticity coordinates: an a* ranging from4 to +4 and a b* ranging from 0 to
 20. 8. The glass composition of claim1, wherein the glass composition, when formed as a glass sheet, has avisible light transmittance of no greater than 80%.
 9. The glasscomposition of claim 1, wherein the total iron in the glass compositionis in the range of 0.2 to 0.8 wt %.
 10. The glass composition of claim1, wherein the glass composition has a redox ratio in the range of0.4-0.6.
 11. The glass composition of claim 1, further comprising acolorant portion comprising: CoO in an amount no greater than 20 ppm; orSe in an amount no greater than 3 ppm.
 12. The glass composition ofclaim 1, wherein the glass composition, when formed as a glass sheet,has a color described by the following chromaticity coordinates: an a*ranging from 8 to −16 and a b* ranging from +3 to
 17. 13. The glasscomposition of claim 1, wherein the colorant portion comprises at leastone of the following: oxides of manganese, tin, cerium, molybdenum,vanadium, copper, zinc, tungsten, and lanthanum, or any combinationthereof.
 14. The glass composition of claim 1 further comprising0.16-0.18 wt. % Fe₂O₃.
 15. The glass composition of claim 1 furthercomprising 0.49-0.58 wt. % Fe₂O₃.
 16. A glass composition comprising abase glass portion comprising: SiO₂ 71.2-71.6 wt. %; CaO 8.3-8.6 wt. %;MgO 5.0-5.2 wt. %; K₂O 0.24-0.25 wt. %; Na₂O 13.4-13.5 wt. %; and Al₂O₃1.1-1.2 wt. %.
 17. The glass composition of claim 16 further comprising0.20-0.21 wt. % Fe₂O₃.
 18. The glass composition of claim 16 wherein theratio of Na₂O to Al₂O₃ is 11.1 to 11.3 wt. %/wt. %.
 19. The glasscomposition of claim 16 wherein the ratio of CaO to MgO is 1.7 to 1.9wt. %/wt. %.
 20. A method of producing a glass sheet comprising: feedingraw batch materials into a container; melting the raw batch materials inthe container to form a molten glass composition; passing the moltenglass composition from the container into a pool of a molten metal suchthat the molten glass composition floats in the pool of molten metal;forming the molten glass composition into the shape of the flat glasssheet on the pool of molten metal; and cooling the molten glasscomposition to form the flat glass sheet, wherein the flat glass sheetcomprises: 65-75 wt % SiO₂; 5-15 wt % CaO; 0-5 wt % MgO; 0-5 wt % K₂O;10-14 wt % Na₂O; and 1-5 wt % Al₂O₃, and wherein the flat glass sheethas a ratio of Na₂O to Al₂O₃ is in the range of 9.5-12.5 wt %/wt %.